Meteorology

Question	Answer
What are the two meteorological factors that we're interested in as pilots?	Air and Water Vapour
What is the temperature change per 1,000 feet?	Roughly 2 degrees celcius
What are the three levels of the atmosphere?	Troposphere, tropopause, stratopause
Explain convection	Convection only occurs in the troposphere. It is the process of rising warm air. When air is heated it becomes lighter that the surrounding air and begins to rise.
What is the tropopause?	It's basically the roof of the troposphere. It varies in height and from day to day and with latitude. It is the point where convection weakens markedly as the air above no longer cools with height. 8km high over poles 18km high over the equator
Explain global circulation	The sun heats the earth most near the equator. The air in contact with the surface becomes hot and starts to rise, this air contains a great deal of water vapour because much of the equatorial region is ocean.
What is the equatorial trough?	A belt of low pressure near the equator. It is cloudy with frequent rain.
What is the sub-tropical ridge?	A belt of high pressure between the tropical and sub-tropical cells. It is relatively free of cloud.
What is the polar front?	A belo of low pressure which separates cold polar air from warmer sub-tropical air. Waves of cold polar air grequently brek free from the polar cell and sweep north to produce cold fronts.
What is the polar high?	The sinking cold air over the poles produces a permanent high pressure region.
What causes the pressure on the earth's surface at any one point?	The weight of the air pressing down. When the air begins to sink (because it's cold), the pressure at surface rises.
What direction does sinking air move in, and why?	Sinking air (high pressure systems, or anticyclones) spiral to the left in the southern hemisphere (anti-clockwise) due to the earth's rotation.
What direction does rising air move in, and why?	Clockwise in the southern hemisphere - again it is due to earth's roation.
Describe the weather in a high pressure system.	Usually stable and relatively cloud free
Describe the weather in a low pressure system. Why is it like this?	The air at the surface flows in to fill the space left by the rising air. This rising air carries water vapour from the surface and as it rises it expands and cools. When it reaches dew point temperature the vapour condenses to form clouds. If sufficient vapour is present to form large clouds, showers and rain areas develop.
What does a synoptic chart tell us?	It is a measure of the surface level pressure, linked by isobars between the points of same SEA LEVEL pressure at each point.
What is the pressure gradient?	Air is drawn to a low pressure region from a high pressure region. When there is a rapid change in pressure, isobars are more closely spaced, the pressure gradient is steep, and winds are strong.
Describe the three features of a synoptic chart	1. A Ridge is a "finger" of high pressure where the wind turns sharply left as it passes through - conditions usually stable 2. A Trough is a "finger" of low pressure where winds turn sharply right. Usually unsettled with rain and thunderstorms. 3. A Col is the area between two highs and two lows. Winds are light, variable with little sig weather
What are some tips for interpreting synoptic charts?	1. Identify one of the pressure systems 2. Mark wind arrows to identify direction of wind (once on any one isobar, it cannot change) 3. Take note of isobar spacing.
What's the difference between gradient wind and surface wind?	Gradient wind is unaffected by surface friction so flows in line with isobars (usually above 3000' AGL). Near the surface wind speed is decreased by friction which gives pressure gradient more time to act on air. Therefore surface wind swings more in favour of the pressure gradient, ie. across the isobars.
What is Ballot's Law?	If a person stands with his back to the wind (in south hem) lower pressure will always be on his right hand
What's the difference between a backing and a veering wind?	You turn left to face a backing wind. You turn right to face a veering wind.
Describe the direction and magnitude of gradient wind to surface wind?	Over land surface wind drops by 2/3 and direction veers by 30 deg Over water it's 1/3 and 10 deg
How does a sea breeze influence wind direction/intensity?	SEA BREEZES occur because solar radiation heats land but water temp doesn't change much. As a result, air on land rises, pulling the cool air from the sea towards it.
How does a land breeze influence wind direction/intensity?	It's basically the opposite of a sea breeze and occurs at night as the land cools but the water is less affected. However the temp difference is not as great and land breeze is more gentle than sea breeze.
How does a katabatic wind influence wind direction/intensity?	Katabatic responds to gravity, not pressure. Ideal condition for katabatic wind are: 1. High plateau sloping steeply down to low terrain 2. Clear skies over plateau 3. Relatively warm surrounding air As the air over the plateau is chilled by conduction with the cold surface it becomes denser/heavier than the surrounding air and flows down the plateau by gravity.
How does a anabatic wind influence wind direction/intensity?	Anabatic winds are basically the opposite of katabatic. As the upper surfaces are heated, it blows "up" the sloping terrain. However are usually of weak force due to need to overcome gravity.
How does a fohn wind influence wind direction/intensity?	This occurs when a wind blowing accross the ocean encouters a mountain barrier close to the coast. The moist wind cools as it rises and the water vapour condense to form cloud on the windward side. The cloud (orographic cloud) releases heat into the environment air. This warm air continues down the lee side of the mountain as a warm dry wind.
What are the three states of water, from lowest to highest energy state?	Ice Liquid Vapour
What is latent heat?	Water must give heat energy out to the environment when changing to a lower energy state, eg. water to ice.
What are the change of state processes?	Solid to liquid is MELTING or FUSION and latent heat must be supplied Liquid to vapour is EVAPORATION and latent heat must be supplied Solid to vapour is SUBLIMATION and latent heat must be supplied. Vapour to liquid is CONDENSATION and latent heat is released Liquid to ice is FREEZING or SOLIDIFICATION and latent heat is released Water vapour to ice is DEPOSITION and latent heat must be released.
What's the relationship between humidity and dew point temperature?	The higher the temperature of the air, the more water vapour that parcel of air can contain. As the temperature of a given parcel of air is reduced at constant pressure, its ability to hold water as vapour reduces.
What is relative humidity?	A measure of how close the air is to saturation.
What is the dew point temperature?	The temperature at which saturation occurs. A parcel of air which is already nearly saturated required only a little cooling to reach saturation.
Explain how the dew point causes rain	Clouds form when the temperature cools to the due point. Further cooling below the dew point causes water vapour to leave the cloud as rain.
Describe atmospheric stability	The atmosphere is stable when rising/sinking air eventually stop rising/sinking of its own accord. Instability exists when rising/sinking air continues to rise/sink of its own accord Atmospheric stability is the way temperature behaves both inside and outside the rising parcel.
What is the environmental lapse rate?	In a standard atmosphere there is a temp drop of 2degC per 1000' of ascent. The ELR largely determines the stability state of the atmosphere.
What causes atmospheric instability?	Any process which causes a rapid drop in temp with height, ie. warming of the lower layers or cooling of the upper layers. There is a high ELR in this case. It is not the temperature itself which causes instability, it is the rate at which temperature changes with height.
What is conditional stability?	Sometimes stability can depend on the humidity of the atmosphere. If humidity is high, cloud is more likely to form. If it's low, less likely. Because the weather depends on condition of atmosphere this state is condition stability.
What is a temperature inversion?	We usually assume that as heigh is increased colder temps will be encountered. This is not always the case, and is a temperature inversion. It is an indication of a very stable atmosphere.
What is a radiation inversion?	At night the surface loses heat to space by terrestrial radiation. A thin layer of air cools by contact with the cold surface, but the warmer air above is almost unaffected. Radiation inversions are unlikely to form on cloudy or windy nights. With cloud the surface doesn't get cold enough. Strong winds mix the air thoroughly with warm air above.
What is a frontal inversion?	When cold air moves in a region previously occupied by warm air, the heavier cold air remains at the surface sliding under the warm air and lifting it.
What is a subsidence inversion?	As the air in a high pressure system leaves the system near the surface, the air above sinks to replace it. As that air sinks, it suffers adiabatic warming due to compression. Almost every high pressure system features and inversion, typically somewhere between 4,000' and 8,000'.
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	Created by Andrew Fisher about 7 years ago